Why does my xbox have a red light?

A few months ago my xbox would shut down after about 40 minutes of gameplay and the light in the center would turn red making the only way to turn it off completely be by plugging it off the wall. Now when I try turning it on, the light on the power brick goes from orange to green for a split second and the xbox's light from green to red as well. The fans on both the xbox and the power brick spin for as log as the lights turn green but then fail and stop spinning.